The present invention relates to power converters, and more specifically, to multiphase power converters.
Radio frequency (RF) system performance requirements are placing tighter noise voltage requirements on the converters that supply power to the RF systems. The noise voltage output from a converter ultimately is imposed on the phase noise of the RF system. For power requirements up to, for example, 2 kW, previous systems often used a single converter. The passive components (inductors and capacitors) of the single converter were large in size and have large parasitic elements. The active devices switch slower as they become larger in order to manage the large parasitics that contribute to the noise voltage. The single converter system is less fault tolerant because the single converter offers a single point of failure.
Multiphase power converters offer a number of advantages over the use of a single converter. In this regard, the use of a plurality of converter cells that are modulated allows the use of smaller passive and active components in each cell as compared to the sizes of the active and passive components for a similarly rated single converter system. Though low pass filters may be used to reduce output noise voltage from a multiphase power converter, the additional components used in a low pass filter reduce efficiency and consume valuable space. Though dither techniques may increase effective pulse width modulated (PWM), dither techniques fail to address reduction in control resolution in multiphase applications.
Multiphase power converters (converters) include two or more interleaved converters or cells that are connected to output a summation of the cell outputs. The cells operate at a common frequency (f) and the phases of the outputs of each of the cells are shifted by control logic. In this regard, for n number of cells, the control logic controls the switching time of each cell to induce a difference in phase angle between the outputs of each cell of 360°/n. The cell outputs are connected in parallel. The output of the converter has an output ripple frequency of n×f.
FIG. 1 illustrates a prior art example of a multiphase power converter (converter) 100. The converter 100 includes n number of cells (e.g., 102a, 102b, . . . 102n). Each cell 102 includes a power stage portion 104 that receives a Vin signal, a current sense portion 106 that senses the current output by the power stage portion 104, an analog-to-digital converter (ADC) 108 that converts the sensed current signal to a digital output, and a current loop compensator 110 that provides a duty cycle signal to the power stage portion 104. The outputs of each of the cells 102 are connected in parallel and output a signal Vout. The Vout signal is converted by another ADC 112 that outputs a digital signal that is biased by a voltage loop compensator portion 114. The voltage loop compensator portion 114 outputs an Iset signal. The current loop compensator portion 110 receives the Iset signal and the signal from the ADC 108 to output the duty cycle signal to the power stage portion 104.